Monitoring apparatus for monitoring an ablation procedure

ABSTRACT

The present invention relates to a monitoring apparatus for monitoring an ablation procedure. The monitoring apparatus comprises an ultrasound signal providing unit for providing an ultrasound signal that depends on received echo series of an object that is ablated. The monitoring apparatus further comprises an ablation depth determination unit for determining an ablation depth from the provided ultrasound signal. The ablation depth can be determined directly from the ultrasound signal and is an important parameter while performing an ablation procedure. For example, it can be used for determining the progress of ablation within the object and for determining when the ablation has reached a desired progression.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/872,037 filed on Jan. 16, 2018, which is a divisional of U.S. patentapplication Ser. No. 13/142,299 filed Sep. 8, 2011, which claimspriority under Section 371 to PCT Application No. PCT/IB2010/050059filed on Jan. 8, 2010, which claims benefit of U.S. ProvisionalApplication Ser. No. 61/144,494 filed on Jan. 14, 2009. Each of theseapplications is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a monitoring apparatus, a monitoring method anda monitoring computer program for monitoring an ablation procedure.

BACKGROUND OF THE INVENTION

The article “In-Vitro Ultrasound Temperature Monitoring in Bovine Liverduring RF Ablation Therapy using Autocorrelation”, Huihua Kenny Chianget al., pages 1439 to 1442, IEEE Ultrasonic Symposium, 2002 discloses anapparatus for determining a two-dimensional temperature distribution inbovine liver tissue based on radio frequency (RF) ultrasound signals.The two-dimensional temperature map is used for thermal dosage controland real-time temperature monitoring during RF thermal therapy.

This apparatus has the drawback that an ablation therapy is not directlymonitored, i.e. the apparatus does not provide direct information aboutthe ablation status of the bovine liver tissue. Only the two-dimensionaltemperature map is determined, which only gives an indirect andinaccurate impression about the ablation status. A control of theablation based on the two-dimensional temperature map is therefore alsoinaccurate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a monitoringapparatus for monitoring an ablation procedure applied to an object moreaccurately. It is a further object of the invention to provide acorresponding monitoring method and a corresponding monitoring computerprogram.

In an aspect of the present invention a monitoring apparatus formonitoring an ablation procedure applied to an object is provided,wherein the apparatus comprises:

an ultrasound signal providing unit for providing an ultrasound signalproduced by

sending ultrasound pulses out to the object,

receiving dynamic echo series after the ultrasound pulses have beenreflected by the object,

generating the ultrasound signal depending on the received dynamic echoseries,

an ablation depth determination unit for determining an ablation depthfrom the provided ultrasound signal.

Since the ablation depth determination unit determines the ablationdepth from the generated ultrasound signal, it is not necessary todetermine a two-dimensional temperature map which yields the abovedescribed inaccurate monitoring of the ablation procedure. Inparticular, the ablation depth can be determined directly from thegenerated ultrasound signal. Furthermore, the ablation depth is animportant parameter while performing an ablation procedure. For example,it can be used for determining the progress of ablation within theobject and for determining when the ablation depth has reached apredefined value, in particular, when a predefined degree oftransmurality has been reached, if the object is a wall, in particular,a wall of a heart. The ablation depth can particularly be used fordetermining when cardiac tissue has become transmural. By determiningthe ablation depth from the ultrasound signal, an important parameter ofablation is accurately determined, thereby improving the accuracy ofmonitoring the ablation procedure.

If an ultrasound pulse is sent out to the object, the ultrasound pulseis reflected at different depths such that echo signals are received bythe ultrasound unit at different times. The echo signals, which aregenerated by reflection of the ultrasound pulse at different depthswithin the object, form an echo series. By considering the speed ofsound and the time, when an echo is recorded after the ultrasound pulsehas been sent out into the object, the echo series can be translatedinto a dependence of an ultrasound reflection property of the object onthe depth within the object.

Furthermore, several ultrasound pulses are sent out to the object atdifferent times, thereby generating echo series at different times.These echo series, which are obtained from different ultrasound pulsesat different times and, thus, which belong to different times, formdynamic echo series. The ultrasound signal which depends on the receiveddynamic echo series represents therefore the ultrasound reflectionproperties of the object at different depths and at different times.

By performing the ablation procedure preferentially a lesion isgenerated in the object. The ablation depth is preferentially defined bythe boundary of the lesion within the object.

By determining the ablation depth at different times, the progression ofablation, in particular, the progression of the lesion boundaryindicating the ablation depth can be determined.

The object is preferentially a heart wall, wherein the tissue of theheart wall is ablated.

The ultrasound signal providing unit can be any unit that provides theultrasound signal. For example, the ultrasound signal providing unit canbe a storing unit in which produced ultrasound signals are stored or itcan be an ultrasound signal receiving unit for receiving a generatedultrasound signal as an input which can be used by the ablation depthdetermination unit for determining the ablation depth from the generatedultrasound signal.

It is preferred that the ablation depth determination unit is adapted todetermine a discontinuity of the ultrasound signal and to determine theablation depth as the depth of the ultrasound signal at which thediscontinuity occurs. In particular, the provided ultrasound signalrepresents ultrasound reflection properties of the object at differentdepths and at different times, wherein the ablation depth determinationunit is adapted to determine a discontinuity of the ultrasound signaland to determine the ablation depth as the depth of the ultrasoundsignal at which the discontinuity occurs.

A discontinuous variation can easily be distinguished from a continuousvariation which generally relates to macroscopic tissue expansion. Thus,the determination of the ablation depth depending on discontinuitiesallows easily and accurately determining the ablation depth.

The ultrasound signal that depends on the received dynamic echo seriescan be represented as a two-dimensional image showing a reflectionintensity depending on two-dimensions, for example, depending on thetime on a horizontal axis and depending on the depth on a vertical axis.This two-dimensional image can also be regarded as a M-mode image. Theablation depth determination unit can be adapted to determinediscontinuities in this two-dimensional image, wherein the ablationdepth at a certain time is determined by determining the position in thetwo-dimensional image, at which the discontinuity has been determined.The ultrasound signal that depends on the received dynamic echo seriescan also be represented as a three- or four-dimensional image showing areflection intensity depending on the time and two or three spatialdimensions, respectively. This allows determining the ablation depth indifferent directions in which ultrasound pulses have been sent out intothe object.

It is further preferred that the provided ultrasound signal representsultrasound reflection properties of the object at different depths andat different times, wherein the ablation depth determination unit isadapted to:

correct the ultrasound signal for a thermal expansion of the objectcaused by the ablation procedure,

determine the ablation depth and an ablation time as the depth and thetime of temporally subsequent signal values of the corrected ultrasoundsignal, which correspond to the same depth and which are not similarwith respect to a predefined similarity measure.

For correcting the ultrasound signal for a thermal expansion of theobject caused by the ablation procedure the ablation depth determinationunit can be adapted to estimate time-resolved shifts, in particular,macroscopic shifts, in the ultrasound signal due to tissue expansion. Inparticular, continuous variations of the ultrasound signal are detectedand used for determining the shifts in the ultrasound signal due totissue expansion for each time for which an ultrasound pulse has beensent out into the object and reflected by the object at differentdepths. Then, the ablation depth determination unit calculates ashift-compensated ultrasound signal to correct for the shift caused bytissue expansion during ablation.

The similarity measure can be determined by calibration measurementswith an object having a known ablation depth. For example, bycalibration a relative threshold can be defined indicating a maximumrelative difference in signal values, in particular, in ultrasoundsignal intensities, leading to the decision that these signal values areregarded as being similar, i.e. a relative difference equal or belowthis maximum relative difference indicates that the corresponding signalvalues are similar.

It is further preferred that the provided ultrasound signal representsultrasound reflection properties of the object at different depths andat different times, wherein the ablation depth determination unit isadapted to:

correct the ultrasound signal for a thermal expansion of the objectcaused by the ablation procedure,

determine stretches comprised of temporally subsequent signal values ofthe corrected ultrasound signal, which correspond to the same depth andwhich are similar with respect to a similarity measure,

determine the ablation depth and an ablation time as the depth and thetime at which the length of the stretches is below a predefinedthreshold.

This predefined threshold can be determined by a calibrationmeasurement, wherein ultrasound signals are generated by sendingultrasound pulses into the object having a known ablation depth. In anembodiment, stretches having a length larger than 0.25 s, furtherpreferred larger than 0.5 s and even further preferred larger than 1 s,are regarded as indicating that an ablation has not yet occurred at therespective depth.

It is further preferred that the ablation depth determination unit isadapted to apply a noise reduction filter on the ultrasound signal forreducing noise of the ultrasound signal. The noise reduction filter ispreferentially a Hilbert filter. The noise reduction filter can also beanother filter like a filter using a band pass, in particular alow-pass, cut-off frequency, or a filter using envelope detection. Thenoise reduction filter filters preferentially high frequencies out ofthe ultrasound signal, in particular, frequencies being larger than thehalf of the frequency of the ultrasound pulse. In an embodiment,frequencies larger 10 MHz are filtered out of the ultrasound signal. Thenoise reduction filter is preferentially adapted to allow reducing noiseand other artifacts in the ultrasound signal. High frequency signalvariations are filtered out by, for example, envelope detection. Thehigh frequency components of the ultrasound signal are typicallyfluctuating due to small changes in temperature, alignment, power,composition of the object, in particular, of the cardiac tissue, etcetera.

It is further preferred that the provided ultrasound signal representsultrasound reflection properties of the object at different depths andat different times, wherein the ablation depth determination unit isadapted to:

correct the ultrasound signal for a thermal expansion of the objectcaused by the ablation procedure,

determine, for different depth regions and at the different times, across correlation of temporally subsequent signal values of the samedepth region,

determine an ablation depth and an ablation time depending on the crosscorrelation of the temporally subsequent signals determined for thedifferent depth regions and at the different times. In particular, theablation depth determination unit is adapted to determine, for differentdepth regions and at the different times, a shift value depending on thedetermined cross correlation and to determine an ablation depth and anablation time depending on the determined shift values, wherein a shiftvalue is indicative of a shift between temporally subsequent signalswithin a depth region.

The ultrasound signal representing ultrasound reflection properties ofthe object at different depths and at different times is preferentiallyan M-mode image.

The cross correlation is preferentially performed in the Fourier domain,i.e. preferentially before determining the cross correlation theultrasound signal is Fourier transformed, and after the crosscorrelation has been determined and before the shift values aredetermined an inverse Fourier transformation is preferentiallyperformed. This performing of the cross correlation in the Fourierdomain results in faster processing.

Preferentially, the depth dimension is subdivided into different depthregions, wherein for each depth region each line of signal valuesdefined by the same time is cross correlated with its temporallypreceding line of signal values which belong to the same preceding time.Thus, for the respective depth region a number of cross correlationlines is determined. The cross correlation lines of the respective depthregion are preferentially averaged. This averaging is preferentiallyperformed by applying an average filter to the cross correlation linesof the respective depth region.

The shift value at a depth region and at a time is preferentiallydetermined by determining a peak of the cross correlation line of therespective depth region at the respective time. The depth position ofthe respective peak within the respective depth region is indicative ofthe shift between the two lines of signal values within the depthregion, which have been cross correlated for determining the crosscorrelation line. The shift value is therefore preferentially determinedfrom the depth position of the peak within the respective depth region.The accuracy of determining the depth position of the peak within therespective depth region is preferentially improved by fitting a parabolato the peak, wherein the maximum of the parabola is used as the depthposition of the peak within the depth region. Preferentially, the peakis cut out of the respective cross correlation line before performingthe fitting procedure, in order to fit the parabola to the peak only andnot to the respective complete cross correlation line within therespective depth region.

For determining the ablation depth and the ablation time a thresholdingis preferentially performed on the determined shift values. In anembodiment, if a shift value is larger than a predefined shiftthreshold, the corresponding depth region and time are preferentiallyregarded as ablation depth, at which the ablation process occurs, and asablation time. A zone where tissue is coagulating corresponds to aregion of poor cross correlation, i.e. corresponds to a region of arelatively large shift value. A healthy tissue zone and a zone includingtissue that is already completely coagulated correspond to regions ofgood cross correlation, i.e. correspond to regions of a relatively smallshift value. The zone at which tissue is actually coagulating cantherefore be separated from a healthy tissue zone and a zone comprisingtissue that is already completely coagulated by using the predefinedshift threshold. This shift threshold can be predefined by, for example,calibration.

The determined shift values can be colored. For example, if the shiftvalue indicates that the two subsequent lines of signal values, whichhave been used for determining the respective cross correlation line,are shifted with respect to each other in a first direction, therespective time and the respective depth region can be colored with afirst color, and, if these two lines are shifted relative to each otherin a second direction being opposite to the first direction, therespective time and depth region can be colored by a second color. In anembodiment, the first color is red and the second color is blue. Theresulting colored image can be shown to a user, in particular, overlaidwith the provided ultrasound signal being preferentially an M-modeimage.

It is further preferred that the ultrasound signal providing unitcomprises an ultrasound unit for

sending ultrasound pulses out to the object,

receiving dynamic echo series after the ultrasound pulses have been sentout to the object,

generating an ultrasound signal depending on the received dynamic echoseries. Thus, the ultrasound signal providing unit itself generates theultrasound signal which is used for determining the ablation depth.

It is further preferred that the monitoring apparatus comprises anablation unit for ablating the object. The ablation unit comprisespreferentially energy application elements like electrodes for applyingelectrical energy, in particular, RF energy, or like optical elementsfor applying light energy, for example, optical fibers. The energyapplication element can also be a cryo-ablation element, a highintensity focused ultrasound element and/or a microwave element. The RFablation electrodes are preferentially unipolar or bipolar. The ablationunit is preferentially arranged in a line or in a curve for ablating theobject along a line or along a curve.

The monitoring apparatus preferentially further comprises an irrigationunit for irrigating a region of the object using, for example, astandard saline solution, in particular, for irrigating an ablatedregion of the object.

It is further preferred that the monitoring apparatus further comprisesa control unit for controlling the ablation unit depending on thedetermined ablation depth. For example, the power and/or duration ofapplying ablation energy to the object can be controlled depending onthe determined ablation depth. If the object is a wall and the thicknessof the wall is known, for example, from a determination of the thicknessby the ablation depth determination unit, the control unit ispreferentially adapted to control the ablation unit depending on thethickness and the determined ablation depth. Preferentially, the controlunit is adapted to ablate a heart wall until the resulting lesion istransmural.

The object is preferentially a heart wall, wherein it is furtherpreferred that the monitoring apparatus is adapted to determine thethickness of the wall and repeatedly the ablation depth, wherein theablation depth determination unit is adapted to determine repeatedly adegree of transmurality of ablation from the determined thickness andthe determined ablation depth. In particular, the monitoring apparatusis adapted to terminate an ablation procedure, if a predetermined degreeof transmurality of ablation has been reached. If the thickness of thewall is modified, for example, by the ablation procedure, preferentiallyalso the determination of the thickness of the wall is also performedrepeatedly.

It is further preferred that the object is a wall, wherein the ablationdepth determination unit is adapted to determine the position of a frontsurface and a back surface of the wall from the ultrasound signal. Inparticular, the ablation depth determination unit is adapted todetermine the thickness of the wall from the determined positions of thefront surface and the back surface of the wall. Thus, the ultrasoundsignal can be used for determining the ablation depth and fordetermining the thickness of the wall, which is preferentially a wall ofa heart, i.e. it is for example not necessary to provide a further unitfor measuring the wall thickness. The thickness of the wall, theablation depth and the degree of transmurality can be determined byusing the ultrasound signal only.

Furthermore, since the ablation depth determination unit is adapted todetermine the thickness of the wall from the ultrasound signal, anablation procedure can be planned based on this determined thickness.

The monitoring apparatus preferentially further comprises avisualization unit for visualizing the ablation depth. In particular,the visualization unit is adapted for visualizing the progression of alesion boundary. The visualization is preferentially performed inreal-time.

It is further preferred that the ultrasound signal corresponds to anultrasound signal that has been produced by directing ultrasound pulsesperiodically in different directions, for example, each ultrasound pulsecan be regarded as an ultrasound beam, wherein the ultrasound beam isswept. Thus, echo series are received in different directions forproducing a spatially two- or three-dimensional ultrasound signal. Thisspatially two- or three-dimensional ultrasound signal is producedseveral times at different times, thereby producing a time-dependentspatially two- or three-dimensional ultrasound signal depending on thereceived dynamic echo series. This allows scanning a larger region. Theablation depth determination unit is preferentially adapted to determinethe ablation depth in one or several directions within a plane or volumecovered by the time-dependent spatially two- or three-dimensionalultrasound signal.

For producing the spatially two- or three-dimensional ultrasound signalthe ultrasound unit preferentially comprises a redirection element forredirecting the ultrasound pulses in different directions. Theredirection element is, for example, a fluid lens, an electromechanicalsteering element, a mechanical rocker probe or another element forredirecting the ultrasound pulse. Furthermore, the redirection elementcan be integrated in a transducer of the ultrasound unit, for example,by using phased-array ultrasound transducers, or a capacitivemicro-machined ultrasound transducer (CMUT) or a piezoelectricmicro-machined ultrasound transducer (PMUT).

The ablation depth is preferentially determined in a direction in whichan ultrasound pulse has been sent out.

It is further preferred that the monitoring apparatus comprises acatheter, wherein the ultrasound unit is located within the catheter.

This allows operating the monitoring apparatus within a hollow objectlike a heart. Furthermore, since the ultrasound can be arranged close toan inner surface of the object, high-frequency ultrasound can be used,if the object is living tissue, although high-frequency ultrasound has asmall penetration depth only.

Preferentially also the ablation unit and/or the redirection element islocated within or at the catheter. Furthermore, an irrigation elementcan also be arranged within the catheter.

The ultrasound unit is preferentially adapted to emit an ultrasoundpulse having a frequency between 10 and 60 MHz, further preferredbetween 15 and 35 MHz.

The catheter preferentially comprises a catheter tip, wherein thecatheter can be adapted to allow ultrasound pulses emitted by anultrasound unit arranged within the catheter to leave the catheterstraight from the tip and/or sideways. Preferentially, the catheter tipis adapted to provide an asymmetrical field of view such that theultrasound pulses can be directed from a forward angle up to a sidewaysangle with respect to a direction along the catheter and pointing to thecatheter tip. This field of view is preferentially achieved by acorresponding opening being, for example, a slot cut out of the cathetertip, wherein a redirection element is located within the opening.

The catheter is preferentially adapted such that the outside of thecatheter is smooth; in particular, the catheter is preferentiallyadapted such that the outside of the catheter tip is smooth. Forexample, the catheter comprises an outside cover covering the catheter,in particular, the catheter tip, such that the outside surface of thecatheter, in particular, of the catheter tip, is smooth.

It is further preferred that the catheter comprises a location sensorfor determining the position and/or orientation of the catheter, inparticular, of the catheter tip. If the ultrasound unit is located at aknown position within the catheter, if the ablation depth is determinedwith respect to the position of the catheter and if the position and/ororientation of the catheter has been determined, the ablation depth withrespect to a desired position and/or orientation of the catheter tip,i.e. of the ultrasound unit, can be determined.

It is further preferred that the monitoring apparatus comprises asensing unit for sensing a property of the object. Also this sensingunit is preferentially arranged within the catheter. The sensing unitcan comprise one or more mapping elements like electrodes for mappingthe electrical activity of the object, which is preferentially a heartwall, or like another sensing element for sensing a property of theobject like an optical element.

The monitoring apparatus preferentially comprises an ablation unitarranged in a line for ablating the object along a line, wherein theultrasound unit is located adjacent to the line. In particular, theablation unit is arranged in at least two lines, wherein the ultrasoundunit is arranged between these at least two lines.

It is further preferred that the monitoring apparatus comprises anablation unit arranged in a curve for ablating the object along a curve,wherein the ultrasound unit is located adjacent to the curve. Inparticular, the ablation unit is arranged in at least two curves,wherein the ultrasound unit is arranged between these at least twocurves.

It is further preferred that the monitoring apparatus comprises anablation unit located at a tip of a catheter, wherein the ultrasoundunit is arranged around the ablation unit.

It is further preferred that the monitoring apparatus comprises anablation unit located at a tip of a catheter and surrounding theultrasound unit.

It is also preferred that the monitoring apparatus comprises a clampingunit including clamp jaws for clamping the object between the clampjaws, wherein at least one of the clamp jaws comprises an ablation unitand wherein at least one of the clamp jaws comprises the ultrasoundunit.

It is further preferred that the ablation depth determination unit isadapted to determine the ablation depth and/or position of the ablationregion with respect to a determined wall surface, if the object is awall, in particular, a heart wall.

In a further aspect of the present invention a monitoring method formonitoring an ablation procedure applied to an object is provided, themonitoring method comprising the steps of:

providing an ultrasound signal produced by

-   -   sending ultrasound pulses out to the object,    -   receiving dynamic echo series after the ultrasound pulses have        been reflected by the object,    -   generating the ultrasound signal depending on the received        dynamic echo series,

determining an ablation depth from the generated ultrasound signal.

In a further aspect of the present invention a monitoring computerprogram for monitoring an ablation procedure applied to an object isprovided, the monitoring computer program comprising program code meansfor causing a monitoring apparatus as defined in claim 1 to carry outthe steps of the monitoring method as defined in claim 13, when thecomputer program is run on a computer controlling the monitoringapparatus.

It shall be understood that the monitoring apparatus of claim 1, themonitoring method of claim 13 and the monitoring computer program ofclaim 14 have similar and/or identical preferred embodiments as definedin the dependent claims.

It shall be understood that a preferred embodiment of the invention canalso be any combination of the dependent claims with the respectiveindependent claim.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter. Inthe following drawings: FIG. 1 shows schematically and exemplarily anembodiment of a monitoring apparatus for monitoring an ablationprocedure applied to an object,

FIG. 2 shows schematically and exemplarily a representation of an echoseries produced by reflections of an ultrasound pulse at heart walltissue,

FIG. 3 shows schematically and exemplarily a two-dimensionalrepresentation of an ultrasound signal that depends on dynamic echoseries,

FIGS. 4 to 8 show schematically and exemplarily representations ofdifferent parts of an ultrasound signal that correspond to differenttime periods before, during and after an ablation procedure,

FIG. 9 shows exemplarily a determined ablation depth and atwo-dimensional representation of the ultrasound signal,

FIG. 10 shows schematically and exemplarily a further embodiment of amonitoring apparatus for monitoring an ablation procedure applied to anobject,

FIG. 11 shows exemplarily a spatially two-dimensional ultrasound signal,

FIG. 12 shows schematically and exemplarily a catheter tip comprising anultrasound unit and an ablation element,

FIG. 13 shows schematically and exemplarily a catheter tip comprising aslot that is cut out of the catheter tip,

FIGS. 14 to 16 show a catheter tip comprising sensing electrodes, asensing and ablation electrode and an ultrasound unit,

FIG. 17 shows schematically and exemplarily a catheter with a cathetertip located within a heart,

FIGS. 18 and 19 show schematically and exemplarily a linear ablation penlocated at a distal end of a catheter,

FIG. 20 shows schematically and exemplarily a lasso ablation cathetertip,

FIGS. 21 and 22 show exemplarily and schematically focal ablation penslocated at a distal end of catheter,

FIG. 23 shows schematically and exemplarily a bipolar clamp located at adistal end of a catheter,

FIG. 24 shows schematically and exemplarily two jaws of the bipolarclamp,

FIG. 25 shows the two jaws of the bipolar clamp clamping tissue,

FIG. 26 shows exemplarily a flowchart illustrating an embodiment of amonitoring method for monitoring an ablation procedure applied to anobject,

FIG. 27 shows exemplarily a further flowchart illustrating a monitoringmethod for monitoring an ablation procedure applied to an object, and

FIG. 28 shows schematically and exemplarily a lesion set in the heart.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows schematically and exemplarily a monitoring apparatus 1 formonitoring an ablation procedure applied to an object. The monitoringapparatus 1 comprises an ultrasound signal providing unit 2 forproviding an ultrasound signal produced by sending ultrasound pulses outto the object, receiving dynamic echo series after the ultrasound pulseshave been reflected by the object and generating the ultrasound signaldepending on the received dynamic echo series. The ultrasound signalproviding unit 2 is, for example, a storing unit in which the ultrasoundsignals are stored for providing them, or the ultrasound signalproviding unit is, for example, an ultrasound signal receiving unit forreceiving ultrasound signals from an ultrasound unit and for providingthese ultrasound signals. The ultrasound signal providing unit 2 canalso be an ultrasound unit for producing the ultrasound signals as willbe explained exemplarily further below.

The monitoring apparatus 1 further comprises an ablation depthdetermination unit 3 for determining an ablation depth from the providedultrasound signal.

If an ultrasound pulse is sent out to the object, the ultrasound pulseis reflected at different depths such that echo signals are received byan ultrasound unit. The echo signals, which are generated by reflectionof the ultrasound pulse at different depths within the object, form anecho series. An echo series 21 is schematically and exemplarily shown inFIG. 2. By considering the speed of sound and the time, at which an echois recorded after the ultrasound pulse has been sent out to the object,the echo series can be translated into a dependence of an ultrasoundreflection property of the object on the depths within the object. InFIG. 2, the amplitude a of the echo series in arbitrary units, whichcorresponds to the ultrasound reflection property, is shown depending onthe depth d in arbitrary units that corresponds to the time, at whichthe respective echo has been received after the pulse has been sent outinto the object.

In this embodiment, the object is a wall of a heart, wherein theultrasound pulse is sent out into the heart tissue of the wall. In FIG.2, the regions of the echo series 21 denote by 22 and 23, correspond tofront and back surfaces of the heart wall. The region 24 is directlygenerated by the ultrasound pulse. Thus, in a strict sense, the echoseries is the graph shown in FIG. 2 without region 24.

The echo series 21 shown in FIG. 2 allows determining the position ofthe front and back surfaces 22, 23 with respect to the position of anultrasound unit that emits the ultrasound pulse and receives the echoes.The first measured amplitude in the region 24 marks the position of theultrasound unit. Region 24 is followed by a region comprising anamplitude being substantially zero and after a while the amplitudeincreases again in region 23 marking the first reflection at the object,i.e. marking the front surface of the object. A region 25 comprisingsmaller amplitudes that correspond to reflections within the tissue ofthe heart wall follows, and then in the region 22 the amplitudeincreases again significantly thereby marking the back surface of theheart wall. Thus, the echo series 21 allows determining the positions ofthe front and back surfaces based on the regions 22 and 23. The region25 in between is used for determining the ablation depth as will beexplained further below.

The ablation depth determination unit is preferentially adapted todetermine the position of the increasing amplitude in region 23 after aregion comprising an amplitude value being substantially zero as theposition of the front surface of the object. Then, the amplitudesubstantially decreases in region 25 and the position of the nextsignificant increase of the amplitude (region 22) is determined as theposition of the back surface of the heart wall. In other words, afterthe ring down of the transducer of the ultrasound unit in region 24 a“quiet period” ensues. This quiet period is subsequently terminated by areflection in region 23 that is associated to the front surface. Afterthis reflection in the region 23 a period 25 occurs that is marked byfast and small temperature changes in the ultrasound intensity. Inparticular, the envelope of the signal in the period 25 tends to have anexponential decrease in intensity. At the end of the period 25 again astrong reflection is observed in the region 22 that is associated to theback surface. Threshold values can predefined, in particular relativethreshold values can be predefined, wherein the front surface isdetected, if a reflection after the “quiet period” exceeds therespective predefined threshold and wherein the back surface isdetected, if at the end of period 25 the signal exceeds the respectivethreshold. The thresholds can be predefined by calibration measurementswith walls having known front surface and back surface positions.

The echo series 21 exemplarily shown in FIG. 2 has been generated by anultrasound pulse that was sent out into the object at a certain time.Several of these ultrasound pulses are sent out to the object atdifferent times, thereby generating echo series at different times.These echo series, which are obtained from different ultrasound pulsesat different times, and, thus, which belong to different times, formdynamic echo series. The ultrasound signal which depends on the receiveddynamic echo series represents therefore the ultrasound reflectionproperties of the object at different depths and at different times.Such an ultrasound signal is schematically and exemplarily shown in FIG.3.

In FIG. 3, different amplitudes of the ultrasound signal are indicatedby different brightness, wherein a higher brightness corresponds tolarger amplitude. The amplitude is shown depending on the depth d andthe time t at which the respective echo series has been generated. Theultrasound signal shown in FIG. 3 forms an image that can be regarded asM-mode image.

By performing an ablation procedure, a lesion is generated in the heartwall, wherein the ablation depth is defined by the boundary of thelesion within the heart wall tissue.

The ablation depth determination unit is adapted to determinediscontinuities in the ultrasound signal and to determine the ablationdepth as a depth of the ultrasound signal at which the discontinuitiesoccur. For example, in FIG. 3 in the first ellipse 26 only continuousvariations of the ultrasound signal are present indicating a macroscopictissue expansion of the heart wall tissue during applying ablationenergy to the tissue. In the second ellipse 27 discontinuities in thevariation of the ultrasound signal can be observed that indicate theablation depth. Thus, FIG. 3 shows the progression of the lesion, i.e.the increasing ablation depth, in the second ellipse 27. Based on theobserved discontinuities the ablation depth is determined as indicatedexemplarily for a certain time by the second double arrow 29, whereasthe first double arrow 28 indicates the thickness of the heart wall fora certain time. It should be noted that also the thickness of the heartwall changes with time during performing an ablation procedure due to amacroscopic tissue expansion as can be seen in FIG. 3.

For determining the ablation depth the ablation depth determination unitcan be adapted to estimate time-resolved shifts, in particular,macroscopic shifts, in the ultrasound signal due to tissue expansion. Inparticular, the continuous variations of the ultrasound signal aredetected and used for determining the shifts in the ultrasound signaldue to tissue expansion for each time for which an ultrasound pulse hasbeen sent out into the object and reflected by the object at differentdepths. Then, the ablation depth determination unit calculates ashift-compensated ultrasound signal to correct for the shift caused bytissue expansion during ablation. In particular, for different times theamplitude values shown in, for example, FIG. 3 are moved vertically incorrespondence with the determined shift for compensating this shiftcaused by tissue expansion. Then, preferentially the ablation depthdetermination unit suppresses noise in the shift-compensated ultrasoundsignal using, for example, a Gaussian filter with, for example, σ=25. Inan embodiment, the ablation depth determination unit is adapted tofollow lines corresponding to a constant depth in the shift-compensatedultrasound signal with time, i.e. to follow horizontal lines in arepresentation of the shift-compensated ultrasound signal thatcorresponds to the representation shown in FIG. 3, until a disjunctiveevent occurs. The length of the horizontal lines before this disjunctiveevent occurs is determined by means of correlation statistics. Then, theablation depth determination unit is adapted to assignablated/non-ablated regions based on the determined lengths of connectedstretches with a cut-off parameter that remains flexible. The cut-offparameter is, for example, 0.25 s. In particular, in a shift-compensatedultrasound image temporally adjacent pixels on a horizontal line arecompared. If along a horizontal line a lesion boundary is not present,the pixels along the horizontal line tend to have roughly the sameintensity and only slow variations may occur. In contrast, if a lesionboundary, i.e. the ablation lesion, reaches the horizontal line, theintensity of the pixels in this line change significantly. The depthassociated with this significant change in the intensity defines theablation depth. Preferentially, the ablation depth determination unit isadapted to determine stretches along a horizontal line comprising pixelvalues having substantially the same intensity. When an ablation frontreaches a certain horizontal line, a significant decrease in the lengthof the stretches in this horizontal line is observed. If the length ofthe stretches is below a predefined threshold, the ablation depthdetermination unit determines the ablation depth as the depth associatedto the location at which the length of the stretches is below thispredefined threshold. This predefined threshold can be determined bycalibration measurements, wherein ultrasound signals are generated bysending ultrasound pulses into the object having a known ablation depth.Also the similarity measure for determining whether adjacent pixelintensity values on a horizontal line are similar or not, i.e. whethertwo adjacent pixel value intensities on a horizontal line belong to thesame stretch, can be determined by this calibration. For example, bycalibration a relative threshold can be defined indicating the maximumrelative difference in the pixel value intensities leading to thedecision that these pixel value intensity values are regarded as beingsimilar, i.e. two pixel value intensities are regarded as being similarif their relative difference is equal to or smaller than the maximumrelative difference that is preferentially determined by calibration. Inan embodiment, stretches having a length larger than 0.25 s, furtherpreferred larger than 0.5 s and even further preferred larger than 1 s,are regarded as indicating that the ablation has not yet occurred at thedepth corresponding to the respective horizontal line.

In a further embodiment, the ablation depth determination unit isadapted to Fourier transform the shift-compensated ultrasound signal inwhich noise has been preferentially suppressed by using, for example, aGaussian filter. The depth dimension is subdivided into different depthregions, wherein for each depth region each line of signal valuesdefined by the same time is cross correlated with its temporallypreceding line of signal values which belong to the same preceding time.Thus, for the respective depth region a number of cross correlationlines is determined. The subdivision of the depth dimension in differentdepth regions corresponds to a sub division in a vertical direction inthe M-mode image shown, for example, in FIG. 3. For example, thevertical lines can be subdivided into about 1000 depth regions. Thenumber of depth regions can be predefined or can be selectedautomatically or by a user, for example, depending on the thickness oftissue to be examined or the ultrasound frequency. Preferentially, forvery thin arterial tissue having a sub-millimeter thickness the numberof depth regions is smaller than 1000 and for very thick ventriculartissue having a thickness being larger than 20 mm the number of depthregions is larger than 1000.

The cross correlation lines of the respective depth region are averaged.This averaging is preferentially performed by applying an average filterto the cross correlation lines of the respective depth region. Theaverage filter has, for example, a filter width of eleven lines.However, the average filter can also have a wider or narrower filterwidth. Moreover, in this embodiment, the ablation depth determinationunit is adapted to apply an inverse Fourier transformation on theaveraged cross correlation lines of the different depth regions and todetermine peaks within the depth regions of the inversely Fouriertransformed cross correlation lines. Thus, preferentially, for eachdepth region and for each time a peak of the cross correlation line isdetermined.

In this embodiment, the ablation depth determination unit is adapted todetermine the depth position of the peak within the respective depthregion by cutting the peak out of the respective cross correlation lineand by fitting a parabola to the cut out peak. The maximum of the fittedparabola defines the depth position of the peak within the respectivedepth region at the respective time.

The ablation depth determination unit is further adapted to determinefor each depth region and for each time a shift value from the depthposition of the peak within the respective depth region at therespective time. Since the peak is a peak of a cross correlation line,the depth position of the peak within the respective depth region isindicative of the shift between the two lines of signal values withinthe depth region, which have been cross correlated for determining therespective cross correlation line. The ablation depth determination unitcan be adapted to determine the depth position of the peak within therespective depth region as the shift value or the ablation depthdetermination unit can be adapted to perform further steps fordetermining a shift value depending on the respective depth position ofthe peak within the respective depth region. For example, predefinedassignments between depth positions of the peak within a depth regionand shift values can be stored in the ablation depth determination unitand used for determining a shift value depending on the determined depthposition of the respective peak within the respective depth region.These assignments can be determined, for example, by calibration.

In this embodiment, the ablation depth determination unit is adapted todetermine an ablation depth and an ablation time depending on the shiftvalues which have been determined for different depth regions and at thedifferent times. For determining the ablation depth and the ablationtime a thresholding is preferentially performed on the determined shiftvalues. If a shift value is larger than a predefined shift threshold,the corresponding depth region and time are regarded as an ablationdepth, at which the ablation process occurs, and as ablation time,respectively. This shift threshold is predefined and stored in theablation depth determination unit and can be determined by calibrationmeasurements.

The ablation depth determination unit can be adapted to color the shiftvalues. For example, if the shift value indicates that the twosubsequent lines of signal values, which have been used for determiningthe respective cross correlation line, are shifted with respect to eachother in a first direction, the respective time and the respective depthregion can be colored with a first color, for example, a blue color,and, if these two lines are shifted relative to each other in a seconddirection being opposite to the first direction, the respective time anddepth region can be colored by a second color, for example, a red color.The resulting colored image can be shown to a user on a visualizationunit 20, in particular, overlaid with the provided ultrasound signalbeing preferentially an M-mode image. The first direction is, forexample, a shift of a vertical line in FIG. 3 within a depth region in adown direction with respect to a preceding line and the second directioncan be a corresponding up direction.

Preferentially, the ablation depth determination unit is adapted toapply a noise reduction filter being a high-frequency filter on theultrasound signal. In this embodiment, the high-frequency filter is aHilbert filter. In another embodiment, the high-frequency filter canalso be another filter like a filter using a band pass cut-off frequencyor a filter using envelope detection. FIG. 3 shows an ultrasound signalon which a Hilbert filter has been applied.

For interpreting the ultrasound signal shown in FIG. 3, the graph can beinterrupted into various parts and re-plotted as exemplarily shown inFIGS. 4 to 8.

In FIGS. 3 to 9 the ultrasound signal for a constant time, i.e. theultrasound signal along a vertical line in these figures, could beregarded as A-line of the ultrasound signal. In FIGS. 3 to 9 theultrasound signal is shown depending on the depth d within the hearttissue wall and the time tin arbitrary units.

In FIG. 4, the ablation procedure is not applied, for example, a radiofrequency ablation electrode is not operated. Thus, the ultrasoundsignal is constant with respect to variations in time, i.e. thereflection properties of the tissue of the heart wall are substantiallynot modified.

Upon ablation, the part of the tissue that is in contact with anablation element, like an ablation electrode at a catheter tip, heats upand the ultrasound signal originating from that region starts to change(FIG. 5). It can also be observed that the heated region expands due tothe thermal load and pushes the yet not heated part of the tissue in adirection that corresponds to a direction from the bottom to the top inFIGS. 3 to 8. In FIGS. 6 and 7 it is shown how the ultrasound signalchanges if the ablation procedure continues. In FIG. 8, the ablationprocedure has been stopped, i.e. the heat source (ablation element) hasbeen switched off, resulting in shrinkage by cooling down and a shift ofthe stripes that correspond to the back surface of the heart tissue wallback towards the original position before ablation. The part of thetissue which was not treated and where no dynamical signal changes areobserved preserves its thickness and just shifts its position.

FIG. 9 shows schematically and exemplarily a line 30 indicating theablation depth determined by the ablation depth determination unit atdifferent times, thereby indicating the progression of ablation. FIG. 9further shows a slide bar 31 indicating the positions of the frontsurface and the back surface of the heart tissue wall by lines 32 and34, respectively, and the ablation depth by line 33 for a certain time.In FIG. 9, the slide bar 31 is shown for the moment when the ablationstops. FIG. 9 can be shown on the visualization unit 20 for visualizingthe progression in ablation.

FIG. 10 shows schematically and exemplarily another embodiment of amonitoring apparatus 101 for monitoring an ablation procedure applied toan object. The monitoring apparatus 101 comprises an ultrasound unit ata distal end of a catheter 12, i.e. at a catheter tip. The ultrasoundunit (not shown in FIG. 10) is an ultrasound signal providing unit andcontrolled by an ultrasound control unit 5. The ultrasound unit and theultrasound control unit 5 are adapted to send out ultrasound pulses toan object 4, to receive dynamic echo series after the ultrasound pulseshave been reflected by the object and to generate the ultrasound signaldepending on the received dynamic echo series. The object 4 is, in thisembodiment, heart wall tissue of a patient 13 to which an ablationprocedure is applied. In another embodiment, the ablation of anotherobject like another organ of a person or of an animal or of a technicalobject can be monitored by the monitoring apparatus.

At the distal end of the catheter 12 an ablation unit for ablating theobject 4 is located. The ablation unit (not show in FIG. 10) comprisesenergy application elements like electrodes for applying electricalenergy, in particular, radio-frequency energy, or like optical elementsfor applying light energy, for example, optical fibers and/or otheroptical elements. The electrodes are preferentially unipolar or bipolar.The energy application elements are preferentially arranged in a line orin a curve for ablating the object along a line or along a curve.

The monitoring apparatus 101 further comprises a sub-control unit 6 forcontrolling the ablation element. The sub-control unit 6 and theultrasound control unit 5 are integrated in a control unit 7. In otherembodiments, the control units can be separate control units.Furthermore, the sub-control unit 6 is preferentially further adapted tocontrol a steering of the catheter tip, a sensing of the heart walltissue and/or an irrigation. In this case, the catheter comprises asteering element, a sensing element and/or an irrigation element,respectively. These different control functions can be performed by anyother number of control units, for example, by a single control unit orby two or more than two control units.

The monitoring apparatus 101 further comprises an ablation depthdetermination unit 103 for determining an ablation depth from anultrasound signal generated by the ultrasound unit. The ablation depthdetermination unit 103 is therefore adapted to receive an ultrasoundsignal from the ultrasound unit and to determine the ablation depth asdescribed above with reference to the ablation depth determination unit3, i.e. the ablation depth determination unit 3 and 103 are similar.

The sub-control unit 6 is adapted to control the ablation unit dependingon the ablation depth determined by the ablation depth determinationunit 103. For example, the power and/or duration of applying ablationenergy to the object 4 are controlled depending on the determinedablation depth. The ablation depth determination unit 103 is adapted todetermine the position of a front surface and a back surface of theheart wall 4 from the ultrasound signal and to determine the thicknessof the heart wall depending on these positions, i.e. the correspondingdepth positions are subtracted from each other to determine thethickness of the heart wall. The sub-control unit 6 is adapted tocontrol the ablation unit depending on this determined thickness and thedetermined ablation depth. Preferentially, the sub-control unit 6 isadapted to ablate the heart wall tissue until a desired degree oftransmurality of the heart wall tissue is reached, in particular, untilthe resulting lesion is transmural.

Preferentially, the monitoring apparatus 101 is adapted to determine thethickness of the heart wall 4 and the ablation depth repeatedly, whereinthe ablation depth determination unit 103 is adapted to determinerepeatedly a degree of transmurality of ablation from the determinedthickness and the determined ablation depth. In particular, themonitoring apparatus 101 is adapted to terminate an ablation procedure,if a predetermined degree of transmurality of ablation has been reached.

Since the ablation depth determination unit 103 is adapted to determinethe thickness of the wall 4 from the ultrasound signal, an ablationprocedure can be planned based on this determined thickness.

The monitoring apparatus 101 further comprises a visualization unit 20for visualizing the ablation depth. In particular, the visualizationunit 20 is adapted for visualizing the progression of a lesion boundary.The visualization is preferentially performed in real-time. Thevisualization unit 20 is preferentially adapted to show the ultrasoundsignal, the progression of ablation, i.e. the lesion boundary, and thefront and back surface positions as schematically and exemplarily shownin FIG. 9. The visualization unit 20 can also be adapted to show theablation depth by just reporting the percentage of transmurality overtime, i.e. in the case of FIG. 9 this would be about 50%.

The ultrasound unit can be adapted to direct ultrasound pulses in onlyone direction or periodically in different directions. For example, eachultrasound pulse can be regarded as an ultrasound beam, wherein theultrasound beam is swept. Thus, echo series can be received in differentdirections for producing a spatially two- or three-dimensionalultrasound signal. A spatially two-dimensional ultrasound signal for acertain time is schematically and exemplarily shown in the upper part ofFIG. 11. The arrows indicated by x and y are two spatial coordinatesdefining spatial positions in the spatially two-dimensional ultrasoundsignal. The broken arrows indicate ultrasound signals at the xpositions, x1, x2 and x3, respectively. In the lower part of FIG. 11,the variation in time at these x positions before, during and after anablation procedure is shown. The ablation depth determination unit 103is preferentially adapted to determine the heart wall thickness and theablation depth at different x positions, in particular, at these three xpositions x1, x2 and x3. Thus, the spatially two- or three-dimensionalultrasound signal is produced several times at different times, therebyproducing a time-dependent spatially two- or three-dimensionalultrasound signal depending on the received dynamic echo series. Thistime-dependent spatially two- or three-dimensional ultrasound signal isused for determining the thickness of the heart wall and the ablationdepth in different directions. This allows scanning a larger region ofthe heart wall tissue.

For producing the spatially two- or three-dimensional ultrasound signal,the ultrasound unit preferentially comprises a redirection element forredirecting the ultrasound pulses in different directions. Theredirection element is, for example, a fluid lens, an electromechanicalsteering element, a mechanical rocker probe or another element forredirecting the ultrasound pulses. Furthermore, the redirection elementcan be integrated in a transducer of the ultrasound unit, for example,by using phased-array ultrasound transducers like a capacitivemicro-machined ultrasound transducer or piezoelectric micro-machinedultrasound transducer.

FIG. 12 shows schematically and exemplarily an embodiment of a cathetertip 135 comprising an ultrasound device 111 within a tube of thecatheter or a catheter shaft 117. The catheter tip 135 further comprisesan ablation element 109 being a radio-frequency catheter electrode. Aguiding element 136 is provided within the catheter for guiding signalsfrom the control unit 7 to the ultrasound unit 111 and back from theultrasound unit 111 to the control unit 7. The guiding element 136 isfurther adapted to guide electrical energy to the ablation element 109.The guiding element 136, which is only schematically shown in FIG. 12,is preferentially comprised of several guiding elements for guidingsignals and energy.

Preferentially, all ultrasound signals are continuously recorded withback-end data acquisition and an image construction instrument.Depending on the clinical needs different imaging devices/configurationscan be employed. For a spatially one-dimensional imaging the ultrasoundunit shown in FIG. 12 is preferentially a single element transducer witha frequency preferably falling between 10 MHz and 30 MHz In anotherembodiment, the ultrasound unit is preferentially adapted to emit anultrasound pulse having a frequency between 10 and 60 MHz, furtherpreferred between 15 and 35 MHz.

The ablation depth determination unit can be adapted to determine theablation depth in different directions. The ablation depth determinationunit can further be adapted to determine the direction in which theablation has progressed furthest, i.e. in which the ablation depth isthe deepest one. A determination of the degree of transmurality can bebased on the ablation depth in this determined direction. Furthermore,the ablation depth determination unit can be adapted to determine anablation region, in particular, the shape and volume, based on thedetermined ablation depth in different directions. In an embodiment,also the ultrasound signal itself can be used to determine a lateralextension of the lesion. The ablation depth in different directions, thedirection in which the ablation depth has progressed furthest, thedetermined ablation region and/or the determined lateral extension ofthe lesion can be stored and/or reported to a user like a clinician, forexample, by using the visualization unit.

The determined ablation depth and thickness of the heart wall can notonly be used to estimate a required ablation power and duration and/orto monitor the lesion formation, but can also be used to verify thelesion after ablation.

The catheter can be adapted to allow ultrasound pulses emitted by theultrasound unit arranged within the catheter to leave the catheterstraight from the tip and/or sideways. Preferentially, the catheter tipis adapted to provide an asymmetrical field of view such that theultrasound pulses can be directed from a forward angle up to a sidewaysangle with respect to a direction along the catheter and pointing to thecatheter tip. This field of view is preferentially achieved by acorresponding opening being, for example, a slot cut out of the cathetertip, wherein a redirection element is located within the opening fordirecting the ultrasound pulses within the asymmetrical field of viewdefined by the opening.

A catheter tip 235 with such an opening 237 providing an asymmetricalfield of view such that the ultrasound pulses can be directed from aforward angle up to a sideways angle with respect to a direction 238along the catheter and pointing to the catheter tip is schematically andexemplarily shown in FIG. 13.

The catheter is preferentially adapted such that at least the outside ofthe catheter tip is smooth; in particular, the catheter ispreferentially adapted such that the outside of the complete catheter issmooth.

FIG. 14 shows schematically and exemplarily a further embodiment of acatheter tip 335. The catheter tip comprises sensing elements 341 being,in this embodiment, sensing electrodes for sensing the heart wall. Thecatheter tip 335 further comprises a sensing and ablation electrode 339including an opening 337 in which an ultrasound unit 311 is located. InFIG. 14 the opening 337 is arranged such that ultrasound pulses can beemitted in a forward direction and in a side direction. FIG. 15 showsthe same catheter tip, wherein the opening 337 is adapted to emit anultrasound pulse in a side direction only. FIG. 16 shows the cathetertip 335 shortly before contacting the object 4, in particular, thetissue of the heart wall. A redirection element 340 is located withinthe opening 337 for directing ultrasound pulses in different directions.In a preferred embodiment, the redirection element 340 is a fluid lensthat allows directing the ultrasound pulses in different directions as afunction of time for generating spatially two- or three-dimensionalultrasound images. This allows determining the ablation depth indifferent directions. The fluid lens preferentially contains twoimmiscible fluids with different speeds of sound, wherein thearrangement of the two fluids within the fluid lens can be modified forchanging the direction of the ultrasound pulse. This modification is,for example, caused by applying a voltage to the fluid lens whichchanges the arrangement of the two immiscible fluids by using theelectrowetting effect.

The monitoring apparatus 101 is preferentially used in combination witha system for determining the position and/or orientation of thecatheter, in particular, within the object 4, preferably, within a heartof a human being or an animal. In this embodiment, an imaging systemlike a magnetic resonance image system or an X-ray fluoroscopy system isused for determining the position and/or orientation of the catheter.This imaging system is indicated by the broken line 8 shown in FIG. 10.The catheter 12, in particular, the catheter tip can comprise elementsfor facilitating the determination of the orientation and/or position ofthe catheter by using the imaging system 8. For example, the cathetertip can comprise a tracking coil, if the catheter tip is used within amagnetic resonance imaging system, or elements that can be identified onan X-ray image and that are shaped such that a determination of theposition and/or orientation of the catheter by using an X-rayfluoroscopy system is possible. The catheter tip can also comprise alocation sensor for determining the position and/or orientation of thecatheter, in particular, of the catheter tip within the object 4.

The positioning systems allows a user to position the catheter 12 withinthe heart, or more specifically, in the left atrium, of a patient. Theuser can position the catheter 12 in the correct position with respectto the heart wall to measure the wall thickness using the ultrasoundsignal generated by the ultrasound unit and the ablation depthdetermination unit. By using the determined position of the cathetertip, i.e. of the ultrasound unit, it is possible to display thethickness of the heart wall in an image of the heart. After collectingsufficient measurements, i.e. after determining the thickness of theheart wall at different locations on the heart wall, the user can thenestablish an ablation strategy including required power and durationdepending on the determined heart wall thickness. It is also possible touse the catheter tip for tracing over the prior-performed ablationlesions for verification purposes. The continuity and depth of thelesions that have been created can be determined.

FIG. 17 shows schematically and exemplarily a heart 342 with atria andventricles, in which a catheter 312 with the catheter tip 335 shown inFIGS. 14 to 16 has been introduced. The heart 342 comprises a septum 343separating the right and left atrium and pulmonary vein openings 344(four in total) in the left atrium.

The catheter can be used during the ablation of tissue of the heartwall. With the catheter, ultrasound scattering from the lesion ismeasured during the ablation, i.e. ultrasound signals are produceddepending on dynamic echo series. Based on the ultrasound signalanalysis performed by the ablation depth determination unit, theposition and depth of the lesion with respect to the heart wall isestablished. In an embodiment, the position of the catheter tip isdetermined with respect to the position where the lesion has beencreated. This determination of the position can be performed by using alocation sensor on the catheter tip combined with triangulation or byusing another method, such as navigation based on imaging such as X-rayimaging or magnetic resonance imaging. Preferentially, the ultrasoundunit in the catheter tip has a field of view which can be in the orderof a view millimeters wide, thereby giving the positioning of thecatheter some tolerance. The monitoring apparatus, in particular, thecatheter, can be used to verify the lesion that is created during theablation procedure.

Preferentially, the catheter tip that comprises the ultrasound unit isin contact with the object while the ultrasound unit sends ultrasoundpulses out into the object. However, the monitoring apparatus can alsobe operated if the catheter tip is not in contact with the object.

Although preferentially the ultrasound unit and an ablation element areintegrated in a catheter tip, i.e. although the ultrasound unit and theablation element are preferentially located at the same side of theobject, for example, the ultrasound unit and the ablation element arepreferentially both located within a heart in front of a heart wall, inan embodiment the ablation unit and the ultrasound unit can be locatedat opposite sides of a wall being the object.

FIG. 18 shows schematically and exemplarily a linear ablation penlocated at the catheter tip 35 of a catheter comprising a catheter tube17. The linear ablation pen 15 comprises a linear ultrasound unit 11located between two linear ablation elements 9, 10 being, in thisembodiment, ablation electrodes. The ultrasound unit 11 and the ablationelements 9, 10 are included in a backbone 14 of the ablation pen 15. Thelinear ablation pen 15 further comprises a pivot element 16 arranged atthe end facing the tube 17 of the catheter for allowing pivoting thelinear ablation pen with respect to the tube 17 of the catheter.

FIG. 19 shows another view of the linear ablation pen 15 arranged on theobject being preferentially a heart wall. The two ablation electrodes 9,10 have created a lesion 18, wherein this lesion 18, in particular theablation depth of this lesion 18, is verified by the ultrasound unit 11comprising the field of view 19.

The linear ablation pen 15 shown in FIGS. 18 and 19 can be used to“draw” lesion lines at an epicardial surface. Instead of two linearablation electrodes 9, 10 only one or more than two ablation electrodescan be integrated into the catheter tip 15. Each of the ablationelectrodes can be unipolar or bipolar. The ultrasound unit 11 cancomprise a series of ultrasound transducers and/or a probe which allowsa spatially two- and/or three-dimensional scanning, such as a phasedarray, a rocker probe, a fluid lens, a machined ultrasound transducer(MUT) array et cetera. If the probe allows spatially two-dimensionaland/or three-dimensional scanning, the probe can be regarded as acombination of an ultrasound unit and a redirection element forredirecting the ultrasound pulses in different directions or the probecan be regarded as an ultrasound unit in which the redirection elementis integrated as it is the case if, for example, a phased array is used.Preferentially, radiofrequency is used for ablating the heart tissue viathe ablation electrodes 9, 10. However, another kind of energy likelight energy can be used for ablation. For example, laser light,microwaves, cryogenic ablation, et cetera can be used for ablation. Thelinear ablation pen and also the other catheter tips described in thispatent application can be constructed with or without an irrigationelement to cool the tissue surface (not shown in FIGS. 18 and 19).

The monitoring apparatus, in particular, the catheter tip, in accordancewith the invention can comprise a sensing element for sensing a propertyof the object. Also the sensing element is preferentially arrangedwithin the catheter, in particular, within the catheter tip. The sensingelement can comprise one or more mapping elements like electrodes formapping the electrical activity of the object, which is preferentially aheart wall, or another sensing element for sensing a property of theobject like an optical element.

FIG. 20 shows schematically and exemplarily a catheter tip being a lassoablation catheter tip 415 arranged on a distal end of a catheter tube417. The lasso ablation catheter tip 415 is curved and comprises twocurved ablation electrodes 409, 410, wherein a curved ultrasound unit411 is arranged between the curved ablation electrodes 409, 410. Theablation electrodes 409, 410 and the ultrasound unit 411 are located ina backbone material 414 of the lasso ablation catheter tip 415. At theend of the lasso ablation catheter tip 415 facing the tube 417 of thecatheter a pivot element 416 is arranged for pivoting the lasso ablationcatheter tip 415 with respect to the tube 417.

The lasso ablation catheter tip 415 can be used to create a lesionaround the pulmonary veins. The lasso ablation catheter tip 415 cancomprise one or more than two ablation electrodes instead of the twoablation electrodes 409, 410. Each ablation electrode can be unipolar orbipolar. The ultrasound unit 411 can be a series of ultrasoundtransducers, or a probe which allows spatially two-dimensional and/orthree-dimensional scanning, such as a phased array, a rocker probe, afluid lens, a MUT array et cetera, as explained above with reference toFIGS. 18 and 19. Also the lasso ablation catheter tip 415 can beoperated with radiofrequency energy for ablation, but alternativelyother energies, in particular, other energy sources, like lasers,microwave sources et cetera can be used for ablation. Also the lassoablation catheter tip can be constructed with or without irrigation tocool the tissue surface.

FIG. 21 shows schematically and exemplarily a focal ablation pen 515located at a catheter tip, in particular, located at the distal end ofthe tube 517 of a catheter. The focal ablation pen 515 comprises acircular ultrasound unit 511 surrounding three electrodes 541 for pacingor sensing, which are arranged at the corners of a triangle and whichsurround an ablation electrode 509. In this embodiment, the circularultrasound unit 511 is centered with respect to the ablation electrode509. The focal ablation pen 515 further comprises a backbone material514 holding the ablation electrode 509, the electrodes 541 for pacing orsensing and the ultrasound unit 511.

FIG. 22 shows schematically and exemplarily another embodiment of afocal ablation pen. The focal ablation pen 615 comprises a circularablation electrode 609 surrounding three electrodes 641 for pacing orsensing that are located at corners of a triangle and that surround anultrasound unit 611. The circular ablation electrode 609 isfocus-centered with respect to the ultrasound unit 611. Also the focalablation element 615 comprises backbone material 614 and is arranged atthe distal end of a tube 617 of a catheter.

The focal ablation pens can be used for the focal ablation ofproarrhythmogenic tissue spots, including ganglionic plexi. The focalablation pen is not limited to a certain number of ultrasound units,ablation electrodes and/or electrodes for pacing and sensing. Eachablation electrode is a unipolar or bipolar electrode. The ultrasoundunit can be a series of ultrasound transducers, or a probe which allowsspatially two-dimensional and/or three-dimensional scanning, such as aphased array, a rocker probe, a fluid lens, a MUT array, et cetera, asdescribes above, for example, with reference to FIGS. 18 and 19. Alsowith the focal ablation pen preferentially a radiofrequency energysource is used for ablation. But, also other energy sources like lasers,microwave sources et cetera can be used for ablation.

If lasers are used as energy sources, of course, instead of ablationelectrodes optical elements like ablation fibers or optical elements fordirecting light to the object are used.

Also the focal ablation pen can be constructed with or without anirrigation unit to cool the tissue surface.

Although the embodiments shown in FIGS. 21 and 22 comprise electrodes541, 641 for pacing and sensing of electrical signals, in anotherembodiment, these electrodes can be omitted. Furthermore, an electrodefor high-frequency pacing can be included to target ganglionic plexi.

FIG. 23 shows schematically and exemplarily a bipolar clamp 715 beingpreferentially located at a distal end of a catheter, i.e. the bipolarclamp 715 forms preferentially the tip of a catheter. The bipolar clamp715 comprises a first jaw 746 and a second jaw 747 being adapted toclamp tissue between the first and second jaws 746, 747. In thisembodiment, the second jaw 747 is fixed to the tube 717 of the catheterand the first jaw 746 is attached to a distal end of a rod 745 slidablyarranged within the tube 717 of the catheter. Thus, by sliding the rod745 towards the distal end of the catheter, tissue can be clampedbetween the first and second jaws 746, 747. Both jaws 746, 747 comprisean ablation electrode 709, 710.

FIG. 24 shows schematically and exemplarily the sides of the first andsecond jaws 746, 747 that face each other, if the two jaws clamp tissue.The first jaw 746 comprises two linear ablation electrodes 709 that arearranged parallel to each other. The second jaw 747 comprises two linearablation electrodes 710 that are arranged parallel to each other,wherein a linear ultrasound unit 711 is arranged between the two linearablation electrodes 710.

FIG. 25 shows schematically and exemplarily the first jaw 746 and thesecond jaw 747 clamping tissue 704. A lesion 718 has been created withinthe tissue 704 by using the ablation electrodes 709, 710 and theultrasound unit 711 verifies the lesion, in particular, generatesultrasound signals for determining the ablation depth. The arrows 719indicate the field of view of the ultrasound unit 711.

The bipolar clamp 715 as shown in FIGS. 23 to 25 can be used to create alesion by clamping tissue between the jaws 746, 747.

In another embodiment, a jaw can comprise only one or more than twoablation electrodes. Furthermore, each jaw can comprise at least oneultrasound unit. The ultrasound unit is preferentially located withinthe second jaw 747 being the lower jaw in FIG. 23. The ultrasound unitcan be a series of ultrasound transducers, or a probe which allowsspatially two-dimensional and/or three-dimensional scanning, such aphased array, a rocker probe, a fluid lens, a MUT array et cetera, asexplained above with reference to FIGS. 18 and 19. Also with the bipolarclamp 715 a radio-frequency energy source is preferred for ablation.But, also other energy sources can additionally or alternatively be usedfor ablation, for example, lasers, a microwave source et cetera. If alaser is used as an energy source, of course, instead of ablationelectrodes optical ablation elements are used, for example, opticalfibers or another optical element for directing light to the tissueclamped between the two jaws. The surface of the jaws 746, 747 ispreferentially atraumatic to prevent acute tissue damage. Thus, thesurface of the jaws is preferentially smooth. The jaws arepreferentially made of stainless steel. The jaws are preferentiallytapered, wherein the cross section of the jaws increases from the endsfacing the tube 717 towards the ends of the jaws pointing away from thistube to facilitate clamp placement and preferentially to not impedevisualization. Furthermore, preferentially the clamped zone of tissue iswider than the zone of ablated tissue, in particular, significant wider.This allows squeezing out blood in the clamped zone out of the ablationzone, thereby reducing the likelihood of thrombus formation.

In the following an embodiment of a monitoring method for monitoring anablation procedure applied to an object will be exemplarily describedwith respect to a flowchart shown in FIG. 26.

In step 801, an ultrasound signal is provided that is produced bysending ultrasound pulses out to the object, by receiving dynamic echoseries after the ultrasound pulses have been reflected by the object andby generating the ultrasound signal depending on the received dynamicecho series.

In step 802, an ablation depth is determined from the generatedultrasound signal.

A further embodiment of a monitoring method for monitoring an ablationprocedure applied to an object is exemplarily described in the followingwith respect to a flowchart shown in FIG. 27.

A catheter tip comprising an ultrasound unit and an ablation element hasbeen introduced into a heart of a human being or of an animal forablating heart wall tissue. The position of the catheter tip has beendetermined. In step 901 the ultrasound unit sends ultrasound pulses outinto the heart wall tissue, receives dynamic echo series after theultrasound pulses have been reflected by the heart wall tissue, andgenerates the ultrasound signal depending on the received dynamic echoseries.

In step 902, the ablation depth determination unit determines thethickness of the heart wall tissue at the position of the catheter tip,and in step 903 ablation parameters are determined based on thedetermined thickness of the heart wall tissue. This determination of theablation parameters can be performed automatically, for example, byusing predefined ablation parameters, which are stored in a storing unitand which are assigned to different heart wall tissue thicknesses andmay be some further parameters influencing the selection of the ablationparameters, for example, the desired shape of the lesion, the locationof the desired lesion within the heart, the age of the patient etcetera. Ablation parameters are, for example, the power and/or durationof the application of ablation energy. Furthermore, as an ablationparameter a degree of transmurality is defined by a user orautomatically determined, for example, by using a look-up table storedin a storing unit.

In step 904, the ablation procedure starts and, while the heart walltissue is ablated, the ultrasound unit produces ultrasound signals whichare used by the ablation depth determination unit for determining theablation depth and thickness of the heart wall tissue. Furthermore, instep 904 the ablation depth and the thickness of the heart wall tissueare visualized on the visualization unit. During the ablation procedure,the ablation depth determination unit calculates the degree oftransmurality and checks in step 905 whether the degree of transmuralitydefined in step 903 has been reached. If this is the case, the ablationprocedure and preferentially also the ultrasound monitoring stop in step906. If the defined degree of transmurality has not been reached, theablation procedure and the determination of the ablation depth and thethickness of the heart wall tissue continue.

The monitoring apparatus can comprise a beam former element for forminga beam defined by the ultrasound pulses. For example, a beam formerelement can be used in conjunction with a phased-array ultrasoundsystem. Several of individually addressable transducer elements can begrouped into one “quasi-pixel”. A possible advantage is the reduction incables. Instead of, for example, 256 cables going to 256 transducers,only 16 cables going to 16 beam former elements may be used, whereineach of the beam former elements drives 16 transducers that are bondedonto them. In particular, directly (cable-less) bonded on them.

The monitoring apparatus is preferentially used in theminimally-invasive treatment of cardiac arrhythmias, whereinpreferentially a radiofrequency (RF) ablation catheter comprising anultrasound unit is used.

The monitoring apparatus allows actively controlling the ablationsettings during treatment. Currently, the therapist relies on his ownexpertise to determine the optimal parameters for ablation, such aspower, temperature, and duration. Note that these settings vary largely,due to sizable intra-patient differences of thickness of the local heartwall, perfusion, blood pressure and velocity, heart rhythm et cetera.Although a highly-skilled therapist is able to achieve successes withthis approach, it is not always the case, and there are seriousconsequences for the patient when an error is made. The two majortherapy-related problems result from either the under-heating or theoverheating of the site. In the case of under-heating, the tissue is notsufficiently coagulated to form the arrhythmia-blocking lesion desiredby the therapist. This can lead to persistent or recurring symptoms inthe patient, and the requirement for subsequent treatment(s), longerperiods of hospitalization, and greater risks of stroke and embolism.The other extreme, overheating, either causes rupturing of the tissue atthe treatment site, releasing potentially life-threatening particlesinto the blood stream, or causes damage to neighboring organs andtissues. In the case that other organs are affected, fistulas candevelop and these are often life-threatening (for example, a fistula inthe oesophagus has roughly a 75% mortality rate).

The monitoring apparatus in accordance with the invention provides amore adequate control of a RF catheter. The monitoring apparatus canprovide feedback of the lesion development in the tissue, and canprovide information about the depth of the lesion with respect to thethickness of the tissue at the treatment site. This allows preventinginjuries and death from under-heating and overheating in RF catheterprocedures.

Surgical ablation of atrial fibrillation (AF) is recommended forpatients with persistent AF undergoing other cardiac surgicalprocedures. The advent of ablation technology has simplified thesurgical treatment of AF, and completion of left atrial lesion setsrequires generally only an additional 10 to 20 minutes operative time.This has increased the interest in ablating AF in patients presented forother surgical cardiac procedures. Note that these open-heart proceduresinvolve generally cardiopulmonary bypass and are performed on anon-beating heart.

More recently, ablation technologies for thoracoscopic and keyholeapproaches have become available allowing epicardial ablation of AF on abeating heart. This minimally invasive epicardial approach circumventsthe need for cardiopulmonary bypass and total procedure times are two tofour hours. However, these procedures do require the deflation of alung, and as such are not trivial.

In the so-called Maze procedure, lesions are constructed to interruptmultiple, disorganized re-entrant currents that characterize AF. Such aprocedure typically includes the isolation of the pulmonary veinscombined with one or more other specific lesion sets. Such a specificlesion set 50 is schematically and exemplarily shown in FIG. 28.

FIG. 28 shows the left atrium 48 comprising the pulmonary veins 49. Theschematic lesion set 50, including bilateral pulmonary veins isolation,is indicated in FIG. 28 by the dashed lines.

Line 52 indicates the mitral valve. Thus, a lesion line is drawn fromthe pulmonary vein openings 49 to the mitral valve. Furthermore, line 51indicates the left arterial appendage. A lesion line is drawn from thepulmonary vein openings 49 to the left atrial appendage 51. In anotherembodiment, line 51 can indicate the septum. FIG. 28 shows a typicalMaze procedure, which includes left atrial appendage exclusion and anisolation line stretching from the pulmonary vein openings encirclinglines to a left atrial appendage exclusion.

For the minimal invasive (thoracoscopic) approach for epicardialablation usually three different electrodes are used for ablation: 1)lasso electrode to create encircling lesion around pulmonary veins; 2)bipolar pen to “draw” ablation lines at the LA roof; 3) ablation pen forablation of ganglionic plexi. The latter has integrated features forhigh frequency stimulation, pacing and sensing. Thus, the ablationsystems described above with respect to FIGS. 18 to 25 arepreferentially used for performing an epicardial ablation.

In general, during the ablation procedure cardiac tissue that is incontact with the energy source, i.e. with the ablation element like anablation electrode, is exposed to high (˜60° C.) or low (˜−50° C.)temperatures such that it is destroyed and a lesion of non-conductingscar tissue is formed. RF is preferentially used as energy source,whereas laser, HIFU, microwave and cryoablation comprise alternativetechniques. The monitoring apparatus in accordance with the invention ispreferentially used to monitor ablation procedures that either destroypro-arrhythmogenic tissue sites or create a continuous and transmuralline of block to prevent an electrical activation from crossing such aline of block.

The different technologies for epicardial ablations can be divided intothose using unipolar energy sources and those that use a bipolar clamp.Bipolar RF ablation with a clamp can overcome some of the limitations ofunipolar devices, including the difficulty of creating transmurallesions due to blood flow in the atrium. With a bipolar clamp, energy isdelivered between two closely approximated electrodes embedded in thejaw of a clamp device resulting in the formation of discrete andtransmural lesions. If an ablation of the right and LA isthmus isrequired, the additional use of unipolar ablation is preferentiallyused.

The monitoring apparatus is preferentially used for monitoring theminimally-invasive procedure of catheter ablation in the left atrium,used to block arrhythmogenic signals in the heart, especially for thetreatment of atrial fibrillation.

In epicardial ablation procedures, the monitoring apparatus allowsobtaining continuous and transmural lesions, even if this is difficultdue to variations in atrial wall thickness and endocardial bloodcooling. In addition, the monitoring apparatus allows providing thetherapist with a direct indication that the lesion has becometransmural. The assessment of transmurality has not to be based onindirect measures including impedance and electrical activity.

The monitoring apparatus can be used for surgical treatment of cardiacarrhythmias and uses ultrasound imaging for establishing the degree oflesion transmurality.

The monitoring apparatus allows determining the progression of the depthof the lesion during the ablation procedure, independent of the energysource used including RF and laser. The monitoring apparatus looks atdynamic changes of the ultrasound signal in time, since the signalchanges most at a zone that corresponds to the tissue region where thetreatment actively happens. The signal at each and every given time canbe compared with the signal recorded at a previous time interval. So,the part of the ultrasound signal that changes most dramatically duringablation can be attributed to the boundary of the lesion whichprogresses through the tissue. In particular, the full time-resolved setof ultrasound data is stored in order to do the analysis and generallysimply subtracting sequential data points (be the A-lines or 2D/3Dimages) will not result in meaningful information.

The monitoring apparatus can be adapted to perform a spatiallyone-dimensional imaging. For instance, the object being, for example,tissue is ablated for 60 seconds at 20 W using a manual unipolar RFcatheter. Single A-lines (as shown in FIG. 2) are recorded with asampling frequency of 20 Hz starting 10 seconds before the ablation andcontinued 20 seconds after ablation. The A-lines are filtered using aHilbert filter and absolute amplitudes after filtering are convertedinto color intensity lines (brightness modulated), which are stitchedtogether such that a two-dimensional graph is obtained. Thistwo-dimensional graph represents the ultrasound signal that depends onthe dynamic echo series of ultrasound pulses sent out into the object.

The invention can be used in tissue imaging during surgical treatment ofcardiac arrhythmias. In these procedures it is desired to createtransmural and continuous lesions in order to block electrical activity.In this invention a monitoring apparatus is proposed that usesultrasound imaging for the direct visualization of the lesion inepicardial ablation. The monitoring apparatus allows using ultrasoundimaging for real-time visualization of the progression of the lesionboundary.

This invention can be used in the field of catheter based cardiacablation. This is especially relevant for catheter treatment of atrialfibrillation. There are at least three different applications for thisinvention: a) Measurement of heart wall thickness: Support for therapyplanning where the ablation energy and duration is based on the measuredheart wall thickness; b) Measurement of the lesion after ablation: Thepurpose is to verify lesion completeness and/or transmurality, when itis still possible for the electrophysiologists to easily go back to theincomplete lesion to add additional ablation points; c) Measurement ofthe created lesion during ablation. Here, the invention is used fortreatment guidance, where the ablation is continued until the lesionmeasurement indicated that the lesion is continuous and/or transmural.

The invention can be used in tissue imaging during treatment of e.g.cardiac arrhythmias and tumor ablation. In these procedures it isdesired to follow the progression of lesion formation during theprocedure.

All arrangements located at a catheter tip disclosed above can be usedwith the monitoring apparatus in accordance with the invention, inparticular, with the monitoring apparatus described above with referenceto FIG. 10.

The monitoring apparatus can comprise any ultrasound unit that allowsgenerating an ultrasound signal depending on received dynamic echoseries after ultrasound pulses have been sent out to the object.

Although in the above described embodiments ablation elements areintegrated together with an ultrasound unit in a catheter, theseembodiments are preferred embodiments only and in another embodiment themonitoring apparatus can comprise a separate catheter including anultrasound unit, wherein the ablation is performed by using anothercatheter.

Although in the above described embodiments certain configurations ofultrasound units, ablation elements and/or sensing elements are shown,the invention is not limited to a certain configuration of ultrasoundunits, ablation elements and/or sensing elements. In an embodiment, themonitoring apparatus does not comprise an ablation element and/or asensing element. Furthermore, the monitoring apparatus does not evenhave to comprise an ultrasound unit. In an embodiment, the monitoringapparatus comprises an ultrasound signal providing unit being, forexample, a storing unit in which the ultrasound signal is stored or anultrasound signal receiving unit for receiving the ultrasound signalfrom an ultrasound unit.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality.

A single unit or device may fulfill the functions of several itemsrecited in the claims. The mere fact that certain measures are recitedin mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

Determinations like the determination of the ablation depth or of aheart wall thickness and/or ablation and/or sensing et cetera performedby one or several units or devices can be performed by any other numberof units or devices. For example, the determination of the ablationdepth or of the heart wall thickness can be performed by a single unitof by any other number of different units. The determinations and/or thecontrol of the monitoring apparatus in accordance with the abovedescribed monitoring method can be implemented as program code means ofa computer program and/or as dedicated hardware.

A computer program may be stored/distributed on a suitable medium, suchas an optical storage medium or a solid-state medium, supplied togetherwith or as part of other hardware, but may also be distributed in otherforms, such as via the Internet or other wired or wirelesstelecommunication systems.

Any reference signs in the claims should not be construed as limitingthe scope.

What is claimed is:
 1. A system for planning an ablation procedure of an organ of a patient, the system comprising: a catheter comprising an ablation element and a catheter tip that houses an ultrasound unit, wherein the catheter tip is configured to be advanced into a vasculature of the patient to a position within the organ; and a computing system coupled to the catheter and configured to determine a thickness of a tissue wall of the organ from reflected ultrasound signals received by the ultrasound unit at the position of the catheter tip within the organ and wherein the computing system is configured to automatically determine an ablation parameter based on the determined thickness of the tissue wall, and to automatically discontinue the ablation procedure when the ablation parameter exceeds a threshold value.
 2. The system of claim 1, wherein the threshold value is a predetermined value based upon the position of a desired lesion within the patient.
 3. The system of claim 1, wherein the computing system is further configured to store a plurality of predefined ablation parameters, and wherein the ablation parameter is determined by comparing the determined ablation parameter to one of the predefined ablation parameters.
 4. The system of claim 3, wherein the predefined ablation parameters are based on at least one of the position of a desired lesion within the organ, and/or an age of a patient.
 5. The system of claim 3 wherein the computing system is further configured to store a look up table of ablation parameters, wherein the threshold value is determined based on the parameters in the look up table.
 6. The system of claim 1, wherein the computing system tracks the position of the catheter tip within the organ based a determination of the position and/or orientation of the catheter tip by using an X-ray fluoroscopy system.
 7. The system of claim 1, wherein the catheter tip comprises a tracking coil, and wherein the computing system tracks the position of the catheter tip within the organ by locating the tracking coil by a magnetic resonance imaging system.
 8. The system of claim 1, further comprising a visualization unit and wherein the system is configured to display the thickness of the tissue wall in an image of the organ at the position for which the respective thickness of the tissue wall has been determined.
 9. The system of claim 8, wherein the thickness of the tissue wall is determined for multiple different locations within the organ.
 10. The system of claim 1, further comprising an ablation unit connected to the ablation element, wherein the computing system is connected to the ablation unit and is configured to transmit the automatically determined ablation parameter to the ablation unit.
 11. The system of claim 1 wherein the ablation parameter comprises a degree of transmurality, and wherein the threshold value is a desired transmurality for the ablation procedure.
 12. A computing system comprising a processor, a non-transitory data storage and an interface to a catheter that is configured to perform an ablation procedure of an organ of a patient, wherein the processor is configured to perform an automated procedure in response to computer-executable instructions stored on the non-transitory data storage, the automated procedure comprising: receiving signals from an ultrasound unit located in the catheter that represent ultrasonic signals reflected from the organ; determining a thickness of a tissue wall of the organ from the received signals; determining an ablation parameter based on the determined thickness of the tissue wall; and automatically discontinuing ablation when the determined ablation parameter exceeds a threshold value for the ablation procedure.
 13. The computing system of claim 12, wherein the non-transitory data storage is configured to store a look up table comprising a plurality of predefined ablation parameters, and wherein the ablation parameter is determined by comparing the determined ablation parameter to one of the predefined ablation parameters.
 14. The computing system of claim 13, wherein the determining of the ablation parameter comprises selecting one of a plurality of predefined ablation parameters assigned to different tissue wall thicknesses.
 15. The computing system of claim 14, wherein at least some of the predefined ablation parameters are based upon a position of a desired lesion within the organ.
 16. The computing system of claim 15, wherein at least some of the predefined ablation parameters are based upon an age of a patient.
 17. The computing system of claim 12 wherein the ablation parameter comprises a degree of transmurality.
 18. The computing system of claim 17 wherein the ablation procedure is automatically discontinued when the determined degree of transmurality exceeds a desired transmurality for the ablation procedure. 